It relates in particular to a yellow-emitting or yellow-green-emitting arrangement of garnet luminescent materials for excitation by means of wavelengths in the blue or near-ultraviolet region of the spectrum. The casting compound provided is in particular a cast-resin matrix containing the arrangement of luminescent materials, and the light source is in particular a light-emitting diode (LED) in combination with the arrangement of luminescent materials and the casting compound.
A luminescent material for light sources and an associated light source are known from WO 98/05078. The light source employed therein is a garnet of the structure A3B5O12:D, in which the first component consists of at least one of various rare-earth metals and component B is one of the elements Al, Ga and In. The dopant D is cerium (Ce).
A similar luminescent material in which either Ce or terbium (Tb) is used as a dopant is known from WO 97/50132. Ce emits in the yellow region of the spectrum, whereas Tb emits in the green. In both cases, the luminescent material is used in combination with a blue-emitting light source to attain a white mixed color.
A wavelength-converting casting compound based on a luminescent material known from the above-cited publications and a transparent casting matrix are known from WO 98/12757. The disclosure content of this document is incorporated herein by reference.
In the production of white mixed light, for example in accordance with WO 97/50132, whose disclosure content, especially with respect to the composition and production of the casting, is also incorporated by reference into this description, it is known to vary the color temperature or the color locus of the white light by appropriate choice, i.e. composition, of the luminescent material, its particle size and its concentration. However, optimization of the hue (color locus X and Y in the CIE chromaticity diagram) of the white light produced is a relatively onerous undertaking. This applies in particular to the so-called achromatic point or “equal energy point” located at the coordinates CIEX=0.33 and CIEY=0.33.
It is also onerous to optimize the luminescent material for the purpose of achieving better color rendition through a larger proportion of red in the spectrum.
Finally, it is difficult to optimize the luminescent material in terms of its absorption maximum relative to the peak value of the emission from the light emitter.